What is scar VT (Ventricular Tachycardia)?

Scar-Related Ventricular Tachycardia (VT)

Scar-related ventricular tachycardia is a form of VT that occurs due to myocardial scarring, which creates the substrate for reentrant circuits, typically resulting in monomorphic VT that may cause significant morbidity and mortality if left untreated. 1, 2

Pathophysiology

• Scar tissue in the myocardium forms the underlying substrate for VT, creating areas of slow conduction that facilitate reentrant circuits 1
• The reentry circuit typically spans several centimeters and can involve endocardial, midmyocardial, or epicardial tissue in a complex three-dimensional structure 1
• The critical isthmus (area of slow conduction) within the VT reentry circuit is the primary target for ablation therapy 1
• Scar-related VT is typically monomorphic, though multiple VT morphologies may be induced in the same patient 1

Common Causes

• Ischemic heart disease (post-myocardial infarction) is the most common cause 2
• Non-ischemic cardiomyopathy 1
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) 1
• Prior cardiac surgery 2
• Cardiac sarcoidosis (less common but important differential diagnosis) 3

Clinical Characteristics

• QRS morphology is determined by the exit site where reentry wavefronts propagate from the scar to depolarize the ventricular myocardium 1
• Typically presents as sustained monomorphic VT 1
• May cause hemodynamic instability, syncope, or electrical storm (recurrent VT/VF with frequent appropriate ICD firing) 1
• Can significantly impair quality of life, especially when associated with ICD shocks 1

Diagnosis

• 12-lead ECG during VT provides valuable information about the exit site of the reentry circuit 1
• Cardiac magnetic resonance imaging (CMR) with delayed enhancement is the preferred non-invasive imaging modality to identify and characterize myocardial scar 1
• Scar size >5% of left ventricular mass is associated with significantly increased risk of arrhythmic events, independent of ejection fraction 1
• Electrophysiological studies with 3D electroanatomical mapping help delineate scar tissue and identify critical isthmuses 1, 4

Management

Acute Management

• Direct current cardioversion is recommended for patients presenting with sustained VT and hemodynamic instability (Class I recommendation) 1
• For stable VT, antiarrhythmic medications may be considered, though electrical cardioversion remains first-line 1

Long-term Management

1. Implantable Cardioverter Defibrillator (ICD)

   • ICDs effectively terminate VT but do not prevent arrhythmia recurrence 1
   • ICD shocks are associated with higher mortality and impaired quality of life 1

2. Catheter Ablation

   • Urgent catheter ablation is recommended in patients with scar-related heart disease presenting with incessant VT or electrical storm (Class I recommendation) 1
   • Catheter ablation is recommended in patients with ischemic heart disease and recurrent ICD shocks due to sustained VT (Class I recommendation) 1
   • Should be considered after a first episode of sustained VT in patients with ischemic heart disease and an ICD (Class IIa recommendation) 1
   • Techniques include:
     • Point-by-point ablation at the exit site of the reentry circuit (scar dechanneling) 1
     • Deployment of linear lesion sets 1, 5
     • Ablation of local abnormal ventricular activity for scar homogenization 1
   • More extensive ablation with creation of linear lesions is associated with better success rates and lower recurrence rates 5

3. Surgical Ablation

   • Surgical ablation guided by preoperative and intraoperative electrophysiological mapping is recommended in patients with VT refractory to antiarrhythmic drug therapy after failure of catheter ablation (Class I recommendation) 1
   • May be considered at the time of cardiac surgery in patients with clinically documented VT or VF after failure of catheter ablation (Class IIb recommendation) 1

Special Considerations

• Epicardial mapping and ablation are more often required in patients with dilated cardiomyopathy or ARVC 1
• Potential complications of epicardial procedures include damage to coronary vasculature, inadvertent puncture of surrounding organs, left phrenic nerve palsy, or pericardial tamponade 1
• Right ventricular scar-related VT is rare but should be considered in patients with left bundle branch block morphology VT and history of right ventricular infarction 6
• Psychological assessment and treatment of distress are recommended in patients with recurrent ICD shocks (Class I recommendation) 1

Prognosis

• Catheter ablation decreases the likelihood of subsequent ICD shocks and prevents recurrent episodes of VT in patients with ischemic heart disease 1
• Beta-blocker therapy combined with amiodarone can reduce the number of ICD shocks, though side effects may limit use 1
• Quality of life issues should be discussed before ICD implantation and during disease progression (Class I recommendation) 1